Fuel cell assemblies convert a fuel and an oxidant to electricity. One type of fuel cell power system employs use of a proton exchange membrane (hereinafter “PEM”) to facilitate catalytic reaction of fuels (such as hydrogen) and oxidants (such as air or oxygen) to generate electricity. The PEM is a solid polymer electrolyte membrane that facilitates transfer of protons from an anode to a cathode in each individual fuel cell normally deployed in a fuel cell power system.
In a typical fuel cell assembly (or stack) within a fuel cell power system, individual fuel cell plates include channels through which various reactants and cooling fluids flow. Fuel cell plates are typically designed with serpentine flow channels. Serpentine flow channels are desirable as they effectively distribute reactants over the active area of an operating fuel cell, thereby maximizing performance and stability. In subzero temperatures, water vapor in the fuel cell assembly may condense. Further, the condensate may form ice in the fuel cell assembly. The presence of condensate and ice may affect the performance of the fuel cell assembly and may also cause damage to the fuel cell assembly.
During typical operation of the fuel cell assembly, waste heat from the fuel cell reaction heats the assembly and militates against vapor condensation and ice formation in the assembly. However, during typical operation conditions, condensate may accumulate at the edges of the fuel cell plates adjacent outlet manifolds thereof, thereby restricting fluid flow from the flow channels through the outlet manifolds. During a starting operation of the fuel cell assembly in subzero temperatures, the condensed water in the flow channels of the fuel cell plates and at edges of the outlet manifolds is in the form of ice within the fuel cell assembly which may result in damage to the fuel cell assembly as reactant flow is restricted. Similarly reactant flow maldistribution due to liquid water stagnation during normal operation can result in damage and instability.
Typically, to militate against the formation of condensation at the outlet manifolds of the fuel cell assembly, the operating temperature of the fuel cell assembly may be increased. However, increasing the operation temperature may have a negative impact on ohmic resistance due to membrane proton resistance as a result of decreased membrane humidification. Also, decreasing the inlet relative humidity of anode and cathode gas streams will achieve the same effect as increasing temperature and may also have have a negative impact on ohmic resistance due to membrane proton resistance.
It would be desirable to develop an apparatus for quickly and efficiently melting ice during start-up of the fuel cell stack in subfreezing temperatures and for heating the fuel cell assembly to militate against water condensation accumulation at the outlet manifolds of the fuel cell assembly and to militate against a subsequent formation of ice in the fuel cell assembly.